Touch-sensitive devices may detect touch via several different mechanisms, including but not limited to optical, resistive, and capacitive mechanisms. Some optical touch-sensitive devices detect touch by capturing an image of a backside of a touch screen via an image sensor, and then processing the image to detect objects located on the screen. Such devices may include a light source within the device to illuminate the backside of the display screen such that objects on the screen reflect the incident light toward the image sensor.
In such devices, the screen may include a diffuser to diffuse light reflected from objects on the screen, as well as to diffuse an image projected onto the screen. The diffuser layer also causes objects lifted from the screen to appear blurry to an image sensor even at close ranges. However, where such a diffuser layer is omitted, it may be difficult to detect whether an object is on or spaced from the screen surface using an image sensor.